Resin bonded abrasive articles containing olivine



United States Patent 3,329,488 RESIN BONDED ABRASIVE ARTICLES CONTAINING OLIVINE Louis L. Cofran, Youngstown, N.Y., asslgnor to The Carborundum Company, Niagara Falls, N.Y., a corporation of Delaware N0 Drawing. Filed July 24, 1964, Ser. No. 385,068

6 Claims. (Cl. 51296) This invention relates to improved bonded abrasive articles. More particularly it relates to improved bonded abrasive articles containing a novel pore-forming material to provide a greater freedom of cut and improved cutting action.

Bonded abrasive articles of the type used in snagging operations are generally in the form of a disc, where the grinding is accomplished on the side or face of the article, or a wheel, where the grinding is accomplished on the periphery. Abrasive articles of this type generally comprise a mass of abrasive granules bonded together by an organic bonding material with or without the presence of fillers and/ or other additives. When abrasive articles, such as discs or wheels of the snagging type are used, it has long been a problem to prevent glazing over of the grinding surface of the article. This glazing over is apparently caused by the softening of the bond material, due to the heat of friction at the grinding interface, with the result that the bonding material flows over the grinding surface and covers the grains of abrasive material thereby interfering with the abrading action of the wheel or disc. Attempts have been made to correct this problem by providing such abrasive articles with holes or pores on the grinding surface so that the article has a cooler cutting action. Thus, open structure and clearance hole-type disc wheels are constantly in demand by industry to provide interrupted and cool cutting action.

Several methods have been used heretofore in an attempt to provide porosity or open structure in disc wheels. In one method the wheel-forming mix is pressed to shape in a mold, the plunger of which has a number of pins or finger-like projections extending into the mold cavity. Thus the wheel is formed having a number of pores or holes throughout the grinding surface. However, it is costly in respect to process and equipment to produce wheels of this type. Moreover such wheels have a non-uniform density, especially where the mix is compressed about the pins. Another method used heretofore in order to obtain porosity has been to incorporate particles of a volatile material, such as naphthalene or paradichlorobenzene, in the wheel forming mix, so that the naphthalene or paradichlorobenzene will volatilize during the curing cycle leaving holes or pores in the wheel. It is extremely difiicult, however, to obtain uniform pore distribution and pore size by such a method.

An object of the present invention is to provide improved bonded abrasive articles.

Another object is to provide bonded abrasive articles having a porous, open structure and free-cutting characteristics.

Another object is to provide a novel pore-forming material which imparts improved cutting action to bonded abrasive articles such as wheels and discs.

A further object is to provide improved bonded grinding wheels in which novel pore-forming material is employed in conjunction with an organic bond.

A further object is to provide a raw batch composition for the manufacture of bonded abrasive articles, the composition containing a novel pore-forming material.

A still further object of this invention is to provide a method for forming bonded abrasive articles having a porous, open structure.

Various other objects and advantages will appear from the following description of an embodiment of the invention, and-the novel features will be particularly pointed out hereinafter in connection with the appended claims.

In accordance with the present invention, organic bonded abrasive articles, such as, for example, disc wheels, are provided with improved abrading and cutting characteristics by incorporating therein during the process of their manufacture, controlled amounts of a novel poreforming material. Thus it has been discovered that disc wheels, and other organic bonded abrasive shapes, of porous, open structure and free-cutting characteristics can be made by the addition to the wheel-forming mix of selected amounts of a friable pore-forming material which is readily removed from the wheel during the grinding operation. The term friable, as used herein, is used in its conventional manner and defines a material which is easily crushed, crumbled, pulverized, or reduced to powder. Thus, when a disc wheel, containing the novel friable pore-forming material of this invention dispersed throughout its grinding surface, is used, such as in removing metal from castings or forgings, the friable pore-forming material breaks down and wears away considerably faster than the abrasive and is readily removed thereby forming holes or pores in the grinding surface of the wheel. This porosity in the surface of the wheel provides an interrupted cut, cool cutting action as well as chip clearance during use.

The novel friable pore-forming material of this invention is olivine. Olivine is an abundant rock-forming mineral group consiting essentially of silicates of magnesium and ferrous iron, that is (Mg, Fe) SiO A complete isomorphous series exists ranging from forsterite, Mg SiO through chrysolite to fayalite, Fe SiO Generally, olivine is richer in magnesium than iron with fayalite being the minor component and usually averaging about 15% of the olivine. Nickel and titanium may be present in minute quantities as impurities. Olivine occurs as orthohombic crystals and is an essential constituent and characteristic mineral or many basic rocks such as gabbro, basalt, peridotite; the rock known as dunite being composed almost Wholly of olivine. Olivine has a specific gravity ranging .3.2 to 4.3, the specific gravity increasing concomitantly with the iron content. It has a hardness of about 6.5 to 7.

Olivine contains from about 36 to about 43 percent silica, from about 28 to about 52 percent magnesia and from about 5 to about 30 percent ferrous iron. The MgzFe of olivine ranges from about 9:1 or higher to about 2:1.

While the use of certain specific, relatively friable materials has been suggested heretofore in conjunction with bonded abrasive articles, such prior art materials have not obtained widespread commercial acceptance. This has been due primarily to the fact that it has been very diflicult to obtain uniform pore distribution with such prior art materials for the pore former tends to segregate from the remainder of the wheel-forming mix. Furthermore such prior art materials tend to adversely affect the strength of the wheels, reducing the strength of wheels to unacceptable low levels.

Olivine, as a friable pore-forming material, is not sube-ct to these limitations and organic bonded disc wheels :ontaining olivine particles as a pore-forming agent do not lave any of these undesirable characteristics. It has been letermined that segregation of the pore-forming agent 1nd the abrasive component of the wheel-forming mix be- :o-rnes desirably less as the density and/or the particle ;ize of these components approach the same value. Since Jlivine has a specific gravity similar to abrasive grain and .s avail-able in particle sizes similar to that of abrasive grain, these characteristics prevent undesirable segregation of the olivine in the wheel-forming mixture. When such a mix is pressed into wheels the olivine is uniformly distributed throughout the wheel so that when the wheel is used and the olivine removed during the grinding operation, there will be a uniform pore distribution throughout the grinding surface. Also, the olivine does not adversely affect the strength of the wheels.

In making organic bonded abrasive articles in accordance with the present invention, conventional abrasive grain, such as silicon carbide and the like, is mixed with a suitable organic bonding material, and a controlled amount of olivine is then added. The bond can be modified by the inclusion therewith of inert or active fillers and/or other modifying agents, as may be desired. The resulting mix is placed in a mold and subjected to pressure to form an abrasive body of the desired shape and size according to conventional manufacturing procedures. The molded article is removed from the mold and subjected to the necessary heat treatment to mature the bond. The times and temperatures required for maturing the bond are those conventionally followed in the making of bonded abrasive articles and depend upon the type of bond used. The organic bonded articles can be either formed by a hot pressing operation in which the bond is partially or fully matured at the time of formation in the mold by simultaneous exposure to heat and pressure, or the articles can be formed by conventional cold pressing techniques, in which the raw batch mixture is pressed to shape in a mold, the body removed from the mold, and the bond subsequently cured by a time-temperature treatment. After curing or firing, the abrasive body is suitably dressed in accordance with conventional practices.

The amount of olivine incorporated in the abrasive body is determined by the degree of porosity desired in the body. The amount may be as large as is practicable to produce a porous article which is also strong enough for the use for which it is intended. In general, the olivine particles may be added to the whee1-forming mix in such an amount that the volume of the olivine is from about 3 percent to about 20 percent of the volume of the molded abrasive body. When more than about 20 percent by volume of olivine is used, undesirable segregation of the olivine and the wheel-forming mix begins to occur. It is preferred, however, that the granular olivine be added in such an amount that it constitutes from about 5 percent to about 15 percent by volume of the bonded article.

In order to provide pores in the wheel, the olivine is employed in particulate form, Granular olivine is available in particle sizes ranging from about 2 mesh to about 50 mesh and finer, and particle sizes within this range may be used in accordance with the present invention. It is preferred that the olivine have a particle size within the range of from about 4 mesh to about +16 mesh (US. Standard Sieve). The optimum amount and particle size of the olivine in the abrasive article in any particular case will depend on conditions of use, such as the nature of the work being ground or cut, the amount of stock to be removed and whether grinding is to be carried out wet or dry, among other factors.

Any of the conventional abrasives, such as silicon carbide, aluminum oxide, zirconia, flint, garnet, bauxite and the like or mixtures thereof can be used in forming the organic bonded abrasive articles of this invention. As used herein, the term organic bond encompasses the natural and synthetic resins, including the phenol-formaldehydes, urea-formaldehydes, melamine-formaldehyde, epoxies, alkyds, polyesters, modified phenolics, natural and synthetic rubbers, shellac and the like. Conventional fillers, such as, for example, cryolite, iron sulfides, fluorspar and the like, in finely divided form may also be included, if desired, in the raw batch composition to be pressed.

When an organic bonded wheel, such as, for example, a resin bonded disc Wheel, containing from about 3 percent to about 20 percent by volume of olivine, is used in a grinding operation, the olivine at the face of the grinding wheel in direct contact with the work being ground breaks down, due to its friability, and is readily removed from the grinding surface of the disc, leaving a hole or pore in the face of the disc. This increased porosity of the working face results in a cool cutting wheel which does not load or bind. If cooling air or a cutting liquid is used in the grinding operation it will be entrained in the open pores and wiped against the face of the work being ground giving a highly effective cooling action. Since the olivine has a density quite similar to that of the abrasive grains commonly used in forming bonded articles, the olivine is uniformly distributed throughout the wheel sothat the pores formed on the grinding face will be generally uniform.

The following specific examples illustrate more clearly the manner in which the novel abrasive articles of the present invention can be prepared. These examples are given for illustrative purposes only, it not being intended to limit the invention to the ingredients, proportions, and processing conditions set forth below.

EXAMPLE I Resin bonded abrasive wheels according to the present invention can be made in the following manner:

Percent Mix: by weight SiC abrasive grain (24 grit) 90.0 Powdered heat hardenable phenolic resin 7.7 Liquid heat hardenable phenolic resin 2.3

The abrasive grain, 24 grit silicon carbide, is first mixed with the liquid phenolic resin in order to wet the abrasive grain. The powdered phenolic resin is then added in increments with continued mixing until all the powdered resin has been taken up and distributed throughout the mixture of abrasive grain. A suitable dry phenolic resin is a phenol-formaldehyde resin known as Varcum 1364. A suitable liquid resin is one known as Varcum 8121. A raw batch composition is then prepared by forming a mixture comprising about percent by weight of the abrasive grain-resin mix prepared above and about 15 percent by weight olivine, the olivine consisting essentially of about 47%-49% MgO 7%9% FeO 39%41% SiO and being uniformly distributed throughout this wheelforming mix. This raw batch composition is then placed in a suitable mold, leveled off and pressed as usual in the formation of disc wheels, to a density of 34 grams per cubic inch. The formed wheel is then removed from the mold and cured in the usual way at a temperature of about 300400 F. for a period of about 40 hours. Disc Wheels, 30" x 1 x 1", made in this manner have an olivine content of about 10 percent by volume. In order to form wheels of this same type having an olivine content of 5 percent by volume, a raw batch composition containing 93 percent by weight of the abrasive grain-resin mix described above and 7 percent by weight of olivine is prepared and placed in a mold and pressed to a density of 33 grams per cubic inch. A wheel of this same type containing 15 percent by volume of olivine is prepared by pressing a raw batch composition containing 79 percent by weight of the abrasive grain-resin mix described above and 21 percent by weight olivine, in a suitable mold to a density of 35 grams per cubic inch. When it is desired to make wheels having a greater or ing Machine, and are based on the average of at least five samples. As a control, a conventional resin bonded, 24 grit silicon carbide test piece containing no poreforming additive was used. This test body was prepared lesser density and/or pore volume it is necessary to and tested in the same manner as the bodies described increase or decrease the amount of olivine in the wheelabove. Fifteen percent additional porosity in this control forming mix accordingly, as is well understood by those piece was obtained through density reduction. The results skilled in the abrasive wheel industry. Disc wheels made of this test are reported in Table II.

TABLE II Amount of Sample Poreiorming Tensile Test and Observation N o. Pore-forming Additive additive Strength Results (percent (p.S.i.) by vol.)

None (15% additional None 855 Slumpage and strength porosity obtained by problem. density reduction). Ball Clay Pellets (ex- 15 717 Reduces strength.

tru'ded). Bauxite (calcined) 15 781 Segregation. Rock salt 15 810 Rust and corrosion problems. Olivine 15 1,006 Satisfactory.

in the manner described above provide interrupted and cool cutting action as well as chip clearance during use.

EXAMPLE II Table I Olivine Bursting strength (Percent by vol.): (s.f.p.m.) 19,400 18,800 10 18,400 17,300 16,400

The strength of these wheels containing from 5 percent to 20 percent by volume olivine was sufiicient to permit-a maximum operating speed, in use, of at least 6,000

s.f.p.m. When olivine was added to the wheel-forming mix in amounts greater than that to provide an article containing 20 percent by volume olivine, segregation of the olivine and abrasive grain-bonding material mix occurred.

EXAMPLE III In order to compare the properties of olivine, against other materials used as pore-forming additives, a number of test bodies were prepared in accordance with the procedure set forth in Example I. Each of these resin bonded, 24 grit silicon carbide test bodies was prepared and pressed under similar uniform conditions, the only differences between the test bodies being the pore-forming material utilized. In each case, suflicient pore-forming material, having a particle size of about 4 mesh and finer was added so that the test body contained 15 percent by volume of the pore-forming additive. Each of the mixes was pressed into a figure-eight briquette of the same size and shape, the briquette having an efiective cross section of one square inch. The wheel-forming mixes and the pressed bodies were evaluated and observed in respect to tensile strength, uniformity of mix, segregation and problems with respect to wheel processing. The tensile strengths were determined under uniform conditions using a Tinius-Olsen Universal Testsive grain size, the specific organic bond, and the proportion of grain to the bond may be varied in accordance with the particular application for which the bonded abrasives are intended. Generally, abrasive bodies of the present invention normally contain more than 50 percent by weight of the abrasive constituent. Similarly the bond pressing and curing conditions will, of course, be dependent on the nature and amount of bonding material used and the intended use of the wheel. Generally, pressures of between about 500 to 6000 psi. are used to press the article while curing is usually accomplished at temperatures of under 500 F. for periods of time up to about 50 hours.

Actual grinding operations with abrasive wheels made in accordance with the present invention demonstrate that the organic bonded wheels are particularly well suited for the grinding of materials which require a porous structure for cool, free-cutting and non-loading of the wheel.

While the present invention has been described in conjunction with preferred embodiments thereof, it is subject to reasonable modifications as will become apparent to those skilled in the art, and such modifications are to be included within the scope of the invention as defined by the appended claims.

I claim:

1. In an abrasive article comp-rising abrasive grains bonded with an organic resin, the combination therewith of a particulate, friable pore-forming material consisting essentially of olivine.

2. The abrasive article as defined in claim 1 wherein said pore-forming material is :present in an amount ranging from about 3 volume percent to about 20 volume percent.

3. The abrasive article of claim 1 wherein said poreforming material constitutes from about 5 volume percent to about 15 volume percent of said article.

4. The abrasive article as defined in claim 1 wherein said pore-forming material has a particle size in the range of from 4 to +16 mesh.

5. The abrasive article as defined in claim 1 wherein said pore-forming material consists essentially of about 7-49 percent MgO, 7-9 percent FeO and 3941 percent iO 6. In a raw batch for the manufacture of a bonded brasive article comprising abrasive grains and an organic esin, the combination therewith of a particulate, friable ore-forming material consisting essentially of olivine, aid olivine being present in an amount sufiicient to contitute from about 3 volume percent to about 20 volume ver-cent of said article and having a particle size in the 'ange of 4 to +16 mesh.

8 References Cited UNITED STATES PATENTS 2,294,239 8/1942 Novotny et a1. 51-298 6 2,333,429 11/ 1943 Kuzmick 51-298 2,592,954 4/ 1952 Robie 51-298 2,729,553 1/1956 Price 51-298 ALEXANDER H. BRODMERKEL, Primary Examiner.

10 D. J. ARNOLD, Assistant Examiner. 

1. IN AN ABRASIVE ARTICLE COMPRISING ABRASIVE GRAINS BONDED WITH AN ORGANIC RESIN, THE COMBINATION THEREWITH OF A PARTICULATE, FRIABLE PORE-FORMING MATERIAL CONSISTING ESSENTIALLY OF OLIVINE. 